Effects of light intensity modulation on PS3-induced resistance of grapevine leaves against Plasmopara viticola

In the context of sustainable viticulture, several methods are currently developed to reduce the use of chemical pesticides. Among them, a strategy based on the activation of defense reactions by the use of elicitors is investigated. Elicitorinduced resistance (IR) is effective in controlled conditions but remains inconsistent in vineyard. Indeed, plant fitness and environmental factors are both likely to affect the plant responsiveness to IR. The aim of this study was to determine the impact of a low light intensity on the resistance induced by sulfated laminarin (PS3) against grapevine downy mildew (Plasmopara viticola). In our conditions, the results showed that control plants acclimated under shade had a percentage of sporulation around two-fold higher than those placed under the limiting light intensity. Otherwise, PS3 had no effect on plant growth or gas exchanges. We also observed that PS3-treated plants had a 1.4-fold higher level of IR against downy mildew when they were grown in shade before inoculation. Interestingly, this higher responsiveness to PS3-IR was correlated with a two-fold greater H2O2 production.